1. Field of the Invention
The present invention relates generally to a three-phase, multi-speed electric induction motor assembly. More specifically, the present invention concerns a three-phase, multi-speed electric induction motor assembly that includes selectable extra winding coil groups that are energized only during a selected speed operating mode to improve balanced motor efficiency between multiple speed operating modes.
2. Discussion of the Prior Art
Those of ordinary skill in the art will appreciate that three-phase electric induction motors are known to be generally effective and are commonly used in a variety of industrial applications. Furthermore, three-phase electric induction motors that can operate at multiple speeds, such as a two-speed motor, may be desirable in certain applications where a load is to be driven at different speeds based upon operational requirements. In order to facilitate two operating speeds for three-phase motors known in the art, power leads of the three-phase motor are typically connected to an appropriate controller that can switch the leads that are connected to a power source to thereby change the effective number of poles (and consequently the speed) of the motor.
Traditionally, either a YY-Δ or a YY-Y winding connection between main winding coil groups has been used to provide a three-phase motor with a low-speed operation mode and a high-speed operation mode, as is generally known in the art. While the YY-Δ and the YY-Y winding connection forms have been satisfactory in some respects, both connection forms present difficulty in balancing both low-speed efficiency and high-speed efficiency, leading to drawbacks in operating costs. Such difficulty in balancing efficiency in both the low-speed mode and the high-speed mode may be particularly detrimental when trying to drive a light load at a very high efficiency.
In a conventional YY-Δ winding connection form for a three-phase, two-speed motor, which is depicted and described in detail below, a pair of main coil groups corresponding to each of the three power phases is provided and the main coil groups are connected to one another as generally known in the art. All of the coil groups are energized during both low-speed and high-speed operation modes. In the YY-Δ winding connection form, the high-speed mode is often too weak, and the low-speed mode is often too strong. Such a connection form thus makes the low-speed operation have a tendency to become very saturated at a light load, leading to a generally lower efficiency during the low-speed mode.
In a conventional YY-Y winding connection form for a three-phase, two-speed motor, which is depicted and described in detail below, a pair of main coil groups corresponding to each of the three power phases is provided and the main coil groups are connected to one another as generally known in the art. All of the coil groups are energized during both low-speed and high-speed operation modes. In the YY-Y winding connection form, the high-speed mode is often too strong, and the low-speed mode is often too weak. Such a connection form thus makes the high-speed operation have a tendency to become very saturated at a light load, leading to a generally lower efficiency during the high-speed mode.
Those of ordinary skill in the art will appreciate that the difference in speed mode efficiencies between the YY-Δ and the YY-Y winding connection forms have required a choice to be made as to which speed mode efficiency is of greater importance in a given application. Even with such a choice, it remains undesirable to suffer a lower efficiency during one of the speed modes, especially when trying to drive a light load at a very high efficiency.